One common application of chromatographic analysis is the use of thermal desorption units to determine the constituents of a particular environment. For example, it is often desired to detect the amount of volatile organic compounds (VOCs) present in a certain sample of air. One way of doing this is by first transporting a sorbent tube packed with an adsorbent material into the environment to be tested, and allowing the VOCs in the air to be collected. In each case, the analytes to be measured (i.e., the VOCs) are retained by the adsorbent as the air passes through the tube.